In order to enhance the safety of occupants of a vehicle, shock-absorbing devices in the form of airbags are, where appropriate, used to reduce the risk of injury on impact. Airbags are pressurized when a collision is detected. In a collision, the occupant will be thrown against the airbag, which is compressed by the impact so that the occupant is gently cushioned by the airbag. After pressurization and compression, the airbag cannot be activated again. This means that conventional airbags are not a suitable choice for protecting the occupants of heavy vehicles such as trucks, for example.
Usual collision sequences involving passenger cars comprise a rapid deceleration of the passenger car so that the occupant is thrown into the airbag. Following this deceleration, the vehicle will usually have been brought to a standstill. A collision sequence involving a heavy vehicle is of an essentially different character to a collision sequence involving a passenger car. This is due to the fact that the motion of the heavy vehicle usually cannot be immediately absorbed by an initial collision but continues to move at somewhat reduced speed following the initial collision. A usual collision sequence involving a heavy vehicle may continue for approximately 10 to 15 seconds. This means that an occupant of a heavy vehicle risks being thrown against the shock-absorbing device a number of times in the course of a collision. Using airbags of known design that are activated and inflated in a collision, a protective function is only provided for the first impact of the sequence. Furthermore, in the pressurization of the airbag, the bag often penetrates the internal lining panel of the vehicle. This can give rise to sharp edges against which the occupant may be thrown at a later stage in the collision sequence.
DE 1 96 47 690 discloses a shock-absorbing device that is designed to be fitted in an enclosed space. The device comprises an outer panel and a gas-filled bag which is fitted to the outer panel. The gas-filled bag is filled after fitting, thereby providing a cushioning assembly. Since the shock-absorbing device is filled in its rest position, there is no risk of the panel being penetrated by pressurization of the flexible container. Since the gas-filled bag is formed from non-rigid material, the container will not assume its original shape after an initial impact. This makes the device unsuitable for multiple impacts during a collision sequence.